The present invention relates to the field of devices for measuring liquid level based on piezoelectric means.
The present invention finds application in particular in the field of the measurement of fuel level/volume in a motor vehicle tank.
Various piezoelectric devices for measuring liquid level, in particular fuel level, have already been proposed.
Regarding this point, reference may be made for example to the documents FR-A-2751744, U.S. Pat. Nos. 5,095,748, 2,753,542, EP-A-0138541, WO-A-91/02950.
More precisely, the present invention relates to devices for measuring liquid level comprising at least one detection assembly (sometimes dubbed a probe or sensor) comprising at least two piezoelectric cells associated with control means for emitting ultrasound waves respectively opposite a reference reflector, situated a known distance from the associated cell on the one hand, and from the upper surface of the liquid on the other hand, and processing means able to determine the level of liquid by utilizing the respective times of propagation of the ultrasound waves emitted by each of these two cells.
The aim of the present invention is to improve the devices of the aforesaid type.
This aim is achieved according to the present invention by virtue of a device of this type comprising means able to define, after the device is switched on, an initialization phase during which the control means operate the piezoelectric cells in such a way that the ratio of the rate of excitation of the reference cell to that of the level measurement is greater than the ratio of these same rates during the subsequent measurement phase.
According to another advantageous characteristic of the present invention, the device furthermore comprises means able to define at least one diagnostic phase during which the piezoelectric cells are isolated from the outputs of the control means and the diagnostic means are sensitive to the signals present on the outputs of these control means.